The mathematical theory of computation (Boolos, Burgess, and Jeffrey 2002) tells us that any problem that can be solved by a series of orderly steps can be solved by a digital computer. The human mind has appeared to many to be just such an all-purpose problem-solver, especially to theorists focusing on such tasks as chess playing; and thus, as the twentieth century wore on, it became increasingly common to think that having a mind is to be an all-purpose computer, or at least to be something near enough.